Saddam Hussein was given a virulent strain of smallpox suitable for use as a biological weapon by a Russian scientist who visited Iraq in 1990, an informant has told the CIA.

The information was considered credible enough to be presented to President George W Bush and hastened White House plans to inoculate a million Americans with the smallpox vaccine. Britain is also planning to inoculate squads of emergency workers, including health professionals and Servicemen.

Nelja Maltseva, a virologist, worked in Moscow´s Research Institute for Viral Preparations for three decades. The institute held 120 strains of smallpox and the variety she is said to have passed to Iraq could be resistant to vaccines.

According to the informant, whose identity is being kept secret, Dr Maltseva travelled to Iraq a dozen years ago. Officials fear that she may have sold the Aralsk strain, named after the port in Kazakhstan where there was a smallpox epidemic in 1971.

The Soviet Union did not report the outbreak to world health officials, and Dr Maltseva, who died two years ago, took part in a covert mission to stop it. She is believed to have taken tissue samples of the strain to her laboratory. She is known to have visited Iraq in 1972 and 1973 and the CIA is trying to establish if a 1990 trip took place.

William Winkenwerder, the US assistant defence secretary for health affairs, told the New York Times that America wanted more help from Russia about the various smallpox strains.

"There is information we would like the Russians to share as a partner of ours," he said. "Because if there are strains that present a unique problem with respect to vaccines and treatment, it is in the interests of all freedom-loving people to have as much information as possible."

Former UN inspectors have said Saddam displayed an increased interest in smallpox vaccines after 1990 and the reason had previously been unknown. (© Copyright of Telegraph Group Limited 2002. 12/04/02)